High speed drilling spindle with reciprocating ceramic shaft and edoubl-gripping centrifugal chuck

Abstract

A spindle capable of operation at 200,000 revolutions per minute (RPM) with a reciprocating shaft design to minimize the moving mass. The spindle has a ceramic spindle shaft to decrease the moving mass and increase the shaft stiffness for better dynamic stability. The spindle employs a built-in linear motor to provide direct drilling motion to move the shaft along the axis, and a permanent magnet DC brushless motor to rotate the spindle shaft. The linear motor is coupled to the shaft by a combination of an air bearing and a magnetic thrust bearing to reduce the size of the thrust area for better dynamic stability and reduction in stresses of material. A double gripping centrifugal chuck is mounted in the hollow ceramic shaft, and reduces drill bit runout.

What is claimed is: 
     
       1. A high speed drilling spindle for a drilling system, comprising: a spindle body;   a rotatable rotor shaft supported within the spindle body for high speed rotation about a rotor axis, said rotor shaft fabricated of a ceramic material capable of withstanding centrifugal forces exerted during high rotation rates without significant diametrical growth of the rotor shaft;   a rotary bearing for supporting the rotor shaft for high speed rotation with low frictional drag within the spindle body; and   a rotary drive system for imparting rotational drive forces to the rotor shaft so as to rotate the shaft on the rotary bearing at high speeds.   
     
     
       2. The spindle of claim 1 further comprising a linear drive system for imparting an axially directed drive force to the rotor shaft to perform drilling movements. 
     
     
       3. The spindle of claim 1 wherein said rotary drive system includes a DC brushless permanent magnet motor, said motor comprising a stator assembly including a plurality of stator windings, said stator assembly mounted within said spindle body, and a permanent magnet mounted within an opening formed in said rotor shaft, the magnet having axially extending north and south magnetic poles which are acted upon by magnetic fields established as a result of excitation signals applied to the stator windings to impart rotational forces to the rotor shaft. 
     
     
       4. The spindle of claim 1 wherein said high rotation rates include 200,000 revolutions per minute. 
     
     
       5. The spindle of claim 1 wherein said rotor shaft includes a hollow tubular structure fabricated of said ceramic material. 
     
     
       6. The spindle of claim 5 wherein said rotary drive system includes a magnet disposed within said hollow tubular structure. 
     
     
       7. The spindle of claim 5 wherein said hollow tubular structure has an outer diameter of 0.7 inch, and an inner diameter of 0.5 inch. 
     
     
       8. A high speed drilling spindle comprising: a spindle body;   a rotatable rotor shaft supported within the spindle body for high speed rotation about a rotor axis, said rotor shaft fabricated of a ceramic material capable of withstanding centrifugal forces exerted during high rotation rates without significant diametrical growth of the rotor shaft;   a rotary bearing for supporting the rotor shaft for high speed rotation with low frictional drag within the spindle body;   a rotary drive system for imparting rotational drive forces to the rotor shaft so as to rotate the shaft on the rotary bearing at high speeds;   a linear drive system for imparting axially directed drive forces to the rotor shaft to reciprocate the rotor shaft along a shaft axis, the linear drive system including a linear motor and a magnetically attracted and air-bearing-repelled thrust bearing for coupling the linear drive system to the rotor shaft, said thrust bearing including an air bearing; and   a centrifugal chuck for holding a tool mounted in a distal end of the ceramic shaft.   
     
     
       9. The spindle of claim 8 wherein the thrust bearing comprises a thrust plate attached at an interior end of the shaft, said linear drive system comprises a magnet attached to a thrust bearing slider structure and positioned adjacent said thrust plate, wherein said magnet and said thrust plate are magnetically attracted to each other, and said thrust air bearing repels said magnetic attraction to prevent said magnet and said thrust plate from coming into contact. 
     
     
       10. The spindle of claim 8 wherein said linear drive system includes a linear drive motor, said linear drive motor comprising an axially movable coil structure having coil windings disposed about the coil structure, a linear motor magnet assembly having core elements fabricated of a magnetic material and one or more permanent magnets, said magnet assembly being stationary with respect to the spindle housing, said coil structure moving axially in response to linear motor drive signals applied to the coil windings. 
     
     
       11. The spindle of claim 10 wherein said coil structure is a cylindrical cupped structure having an open end and a closed end, said coil windings disposed about a periphery of said cupped structure. 
     
     
       12. The spindle of claim 8 herein said shaft comprises a hollow ceramic tube structure, and said chuck is disposed within a sleeve member inserted into said distal end of said ceramic shaft, said sleeve member fabricated of a metal material to relieve localized stresses exerted by the chuck on the ceramic shaft. 
     
     
       13. The spindle of claim 8 wherein said rotary drive system includes a DC brushless permanent magnet motor, said motor comprising a stator assembly including a plurality of stator windings, said stator assembly mounted within said spindle body, and a permanent magnet mounted within an opening formed in said rotor shaft, the magnet having axially extending north and south magnetic poles which are acted upon by magnetic fields established as a result of excitation signals applied to the stator windings to impart rotational forces to the rotor shaft. 
     
     
       14. The spindle of claim 13 wherein the rotor shaft is a hollow ceramic tube having a central opening formed therethrough, and said permanent magnet is disposed within said hollow opening. 
     
     
       15. The spindle of claim 8 wherein said high rotation rates include 200,000 revolutions per minute. 
     
     
       16. The spindle of claim 8 wherein said rotor shaft includes a hollow tubular structure fabricated of said ceramic material. 
     
     
       17. The spindle of claim 16 wherein said rotary drive system includes a magnet disposed within said hollow tubular structure. 
     
     
       18. The spindle of claim 16 wherein said hollow tubular structure has an outer diameter of 0.7 inch, and an inner diameter of 0.5 inch. 
     
     
       19. A centrifugal chuck for use in a spindle, holding a tool having a tool shank in place during high speed rotation to perform tool operations, the chuck adapted to grip the drill shank during rotation at first and second separated points along the shank to guarantee parallelism of the shank to the axis of rotation, the chuck comprising a uni-body flexure which has two gripping segments, the first gripping segment at a front end of the chuck and the second gripping segment at a back end of the chuck, each gripping segment including a plurality of weights distributed about the chuck axis and which are joined by flexures to form a uni-body construction. 
     
     
       20. The chuck of claim 19 wherein said plurality of weights for said first gripping segment consists of four weights segments joined adjacent a first gripping end of the chuck by a first set of corresponding flexures, and said plurality of weights for said second gripping segment includes four weights segments joined adjacent a second gripping end by a second set of corresponding flexures. 
     
     
       21. The chuck of claim 19 wherein said joining flexures are disposed well away from the longitudinal center of mass of the respective weights, permitting movement of the weights in a pivoting action in response to centrifugal forces. 
     
     
       22. The chuck of claim 19 wherein the front and back gripping segments are connected with each other by a plurality of thin wall flexures. 
     
     
       23. The chuck of claim 19 wherein each of said weights includes a gripping end, and each of said two gripping segments includes a pivot ring protruding from the flexures joining the plurality of weights, and each of said plurality of weights, when exposed to the spindle rotation, is subjected to centrifugal force which moves it outward, rotating around the pivot ring, and during this motion the gripping end of the weight is pivoted inwardly, closing on a tool shank to apply force on the tool shank. 
     
     
       24. The chuck of claim 23 wherein the pivot ring has an outer surface protruding slightly from an exterior surface of the chuck. 
     
     
       25. The chuck of claim 19 further including a compressive element installed into a groove formed in the uni-body chuck to frictionally engage the shank and retain the tool in the centrifugal chuck when it is not rotating. 
     
     
       26. The chuck of claim 23 wherein the pivot ring of the first gripping segment has a slightly larger outer diameter than a corresponding outer diameter of the gripping ring of the second gripping segment. 
     
     
       27. A high speed drilling spindle for a drilling system, comprising: a spindle body;   a rotatable rotor shaft supported within the spindle body for high speed rotation about a rotor axis, said rotor shaft fabricated of a ceramic material capable of withstanding centrifugal forces exerted during high rotation rates without significant diametrical growth of the rotor shaft;   a rotary bearing for supporting the rotor shaft for high speed rotation with low frictional drag within the spindle body;   a rotary drive system for imparting rotational drive forces to the rotor shaft so as to rotate the shaft on the rotary bearing at high speeds;   a linear drive system for imparting an axially directed drive force to the rotor shaft to perform drilling movements; and   a thrust bearing for coupling the linear drive system to the rotor shaft, said thrust bearing including an air bearing and magnetically-attracted thrust surfaces.   
     
     
       28. The spindle of claim 27 wherein the magnetically-attracted thrust surfaces comprise a thrust plate attached at an interior end of the shaft and a magnet attached to a thrust bearing slider structure and positioned adjacent said thrust plate, wherein said magnet and said thrust plate are magnetically attracted to each other, and said air bearing repels said magnetic attraction to prevent said magnet and said thrust plate from coming into contact. 
     
     
       29. A high speed drilling spindle for a drilling system, comprising: a spindle body;   a rotatable rotor shaft supported within the spindle body for high speed rotation about a rotor axis, said rotor shaft fabricated of a ceramic material capable of withstanding centrifugal forces exerted during high rotation rates without significant diametrical growth of the rotor shaft;   a rotary bearing for supporting the rotor shaft for high speed rotation with low frictional drag within the spindle body;   a rotary drive system for imparting rotational drive forces to the rotor shaft so as to rotate the shaft on the rotary bearing at high speeds;   a chuck for holding a tool mounted in a distal end of said ceramic shaft; and   wherein said shaft comprises a hollow ceramic tube structure, and said chuck is disposed within a sleeve member inserted into said distal end of said ceramic shaft, said sleeve member fabricated of a metal material to relieve localized stresses exerted by the chuck on the ceramic shaft.   
     
     
       30. A high speed drilling spindle for a drilling system, comprising: a spindle body;   a rotatable rotor shaft supported within the spindle body for high speed rotation about a rotor axis, said rotor shaft a hollow tube having a central opening formed therethrough and fabricated of a ceramic material capable of withstanding centrifugal forces exerted during high rotation rates without significant diametrical growth of the rotor shaft;   a rotary bearing for supporting the rotor shaft for high speed rotation with low frictional drag within the spindle body; and   a rotary drive system for imparting rotational drive forces to the rotor shaft so as to rotate the shaft on the rotary bearing at high speeds, said rotary drive system including a DC brushless permanent magnet motor, said motor comprising a stator assembly including a plurality of stator windings, said stator assembly mounted within said spindle body, and a permanent magnet mounted within said tube central opening, the magnet having axially extending north and south magnetic poles which are acted upon by magnetic fields established as a result of excitation signals applied to the stator windings to impart rotational forces to the rotor shaft.   
     
     
       31. A high speed drilling spindle for a drilling system, comprising: a spindle body;   a rotatable rotor shaft supported within the spindle body for high speed rotation about a rotor axis, said rotor shaft fabricated of a ceramic material capable of withstanding centrifugal forces exerted during high rotation rates without significant diametrical growth of the rotor shaft;   a rotary bearing for supporting the rotor shaft for high speed rotation with low frictional drag within the spindle body;   a rotary drive system for imparting rotational drive forces to the rotor shaft so as to rotate the shaft on the rotary bearing at high speeds; and   a linear drive system for imparting an axially directed drive force to the rotor shaft to perform drilling movements, said linear drive system including a linear drive motor, a thrust bearing slider structure and a thrust bearing for coupling the thrust bearing slider structure to the rotor shaft, said linear motor drive comprising an axially movable coil structure having coil windings disposed about the coil structure, a linear motor magnet assembly having core elements fabricated of a magnetic material and one or more permanent magnets, said magnet assembly being stationary with respect to the spindle housing, said coil structure moving axially in response to linear motor drive signals applied to the coil windings.   
     
     
       32. The spindle of claim 31 wherein said coil structure is a cylindrical cupped structure having an open end and a closed end, said coil windings disposed about a periphery of said cupped structure. 
     
     
       33. The spindle of claim 32 wherein said linear motor magnet assembly is supported within said open end of said cupped structure. 
     
     
       34. The spindle of claim 1 further comprising a chuck for holding a tool mounted in a distal end of said ceramic shaft.